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noticed a little mold/mildew around one of my vents, and tried to find a water leak. I couldn't find any, but while trying to diagnose it I noticed my humidity level in the house is pretty high - about 50-55%. I'm in Dallas, and the outside humidity is about 32% currently, but my inside humidity is about 55%. My system is 2Bryant 2.5 ton systems (zoned one per story), in a 2 story 2600 sq ft home. The house is about 5 years old. The humidity doesnt' really change much if I run the system for extended periods or just normally. I called a service company, they came out and did a check. They weren't real sure about the humidity, but they said that an issue I had was low air flow. They claimed for my 2.5 ton system I should be getting 1000cfm, they were only seeing 700. They said my 20x20 return with a 14" duct was too restrictive, and for $1000 they'll add another 2 10" returns to increase the airflow. They weren't real sure if this was my humidity issue or not, but felt that it would probably fix it. He said everything seemed fine across the coil, and that the CFM issue was the only real thing he could find. Of course, i'll get a 2nd opinion before committing to that kind of work on a fairly new system. Any ideas on my humidity problem? It's usually 34% or so at work with a pretty old system on 73 degrees. No matter what I set mine to I just can't get below 50%. I'm worried about mold issues, and why mine won't dehumidify in general. They lowered the blower speed from high to med-high to try and get it colder across the coil, but it didn't seem to help. I think he was saying because of the airflow issue he couldn't charge it as much as he thought it should be, but he was pretty deep into superheat technical talk and most of it was over my head. $215 later they still don't seem know why mine system won't dehumidify.

Hopefully they checked to see if condensate was blowing off of the surface of the cooling coil or not ; ive had this happen a few times in my travels . Your homes foundation might be laden with moisture creating high humidity within the home...especially after a heavy rainstorm. If you have a furnace mounted humidifier, make sure the solenoid valve isnt stuck letting water in the humidifier then into the airstream - had this happen just the other day on a job. Also, if you cook alot or take showers alot, you can expect your indoor humidity to be higher than normal. Another frequent cause of high humidity in a house, is a grossly oversized Cooling System which cools so fast that it doesnt run long enough to dehumidify properly. If all of the above have been looked at closely, then, obtaining a Portable Dehumdifier such as a Sears Brand 50 pint per day capacity unit...should help quite a bit.

thx for the follow ups

Ground slope was adequate during the inspection ( I remember him going over that specifically). There's no crawl, it's a slab foundation (no basements here either). There hasn't been any rain in quite some time. I don't think there's a humidifier at the furnace. The system doesn't run all that hard, but it does run for good 30 -60 minute stretches. I tried putting it down to 67 just go get a good run time on it , and it didn't help at all. My humidity goes down a tad if I open all the windows and crank the exhaust fans. As for a dehumidifier, shouldn't the AC be doing that? 55% when it's 32% outside is pretty abnormal, isn't it? It's a pretty dry climate here. When I put the hygrometer up to the vent with the AC on, it starts climbing pretty quick .

If your system is running for 60 minute stretches between normal cycles...i would highly suspect that the system is undercharged of refrigerant and/or that the entire system needs 'properly' servicing including : thorough cleaning of the Condensor Coils and Cooling Coils. Further, the Tech should make absolutely sure that the Cooling COil is sealed tight so no air bypasses around the Coil --- this is very typical of hack installations and of course does contribute to a large quantity of air not being conditioned . Id obtain a good Tech to come out .

Originally posted by beenthere You have low air flow, so he slowed down the blower?

Need to have your duct checked for air leaks.

He said he thought that might get it colder across the coil and help the dehumidification. He didn't have a way to check for leaks that I could tell, he did apply some duct sealant to an area that had some loose caulk in the return. He didn't know if it was leaking or not. He checked the refrigerant, but said he couldnt' add more because of the airflow issue, and superheat technobabble, and that it would liquidify, bleah. So basically it was "spend this 1000 bucks to fix your airflow problem"

anyone know of good ole cagey tech in the dallas area? I'm a little north in McKinney. this has been very frustrating. I see some of you guys talking about trying different size coils and bulb locations. That's the guy I want. The tech that came out was from a respected local company, but I think he was pretty new to the field. $215 later all I have is an estimate for $1000.

Originally posted by beenthere You have low air flow, so he slowed down the blower?

Need to have your duct checked for air leaks.

Sounds overs sized.

Set the down stars stat, about 6° warmer then the upstairs, and see if that makes a difference this weekend.

Questions, if it's oversized, is it just lack of run time that keeps it from dehumidifying? When I cranked it down to 67 to make it run a while it didn't help either. I'm trying your 6* test now. upstairs is 72, I'll put down on 78. How'd you get the little degree o up there by the way?

if the humidity is higher inside the house than outside, you have to find the source of humidity. as hvacfella said, showers and cooking could be the cause, but you could also have more serious problems like a plumbing leak or cracks in your foundation

thanks.

I've been running the exhaust fans lately. I didn't know you should run them really, until I started digging into this problem. My humidity today is about 54% inside, but it's 58% outside so I'm on the right side of the battle for a change. When I put my hygrometer up in a vent, it starts shooting up really fast. It'll top out to 99% in pretty short order. I'm really hoping this is just an HVAC problem, the foundation cracks and leaky plumbing don't sound very fun (or cheap) to troubleshoot. I've turned off my sprinkler system, and I'll leave that off for a while to see if that impacts the issue.

I'll run through that sizing in a bit. Thanks so much for the help. Would a properly sized system or a whole house de-humidifyer be the better bang for the buck? I saw the Ultra-Air 100v that looked like it would be a nifty solution, but I haven't seen pricing anywhere. Is the properly sized unit just a coil swap, or does the whole shibang have to be replaced?